[linrad] Re: Sound card sample delay

[Alberto di Bene <usa.net; dibene@xxxxxxxxxxxxxxxx>]

John Harrison, NI1B wrote:
>    However, with newer sound cards basically cheap PCI ones, occasionally
> Linrad/Knoppix/sound driver would under certain circumstances skip sound
> samples. So the whole FFT image would mirror image. A little while later
> it would reverse again. It was never stable enough to allow calibrating. 
> So, I probably wouldn't have noticed the lack of cancellation effect you
> speak of.

 Hi all,

  what you have experienced John is still another variation on the theme. There are some sound cards, mainly from 
Creative, but also from other brands, that *do* delay one channel by one sample constantly with respect to the other.
Many hypothesis have been done about the why. Maybe they have a cheap ADC with just one channel which is multiplexed 
between the left and the right audio channels... just a guess... or some drivers have a common base code with that error 
in it... who knows...

Anyway if you are unlucky enough to have one of those cards, you must compensate in software for that delay. It is not 
difficult, a few instructions and an extra position in the input buffer. Only after this compensation the normal image 
rejection routine can be applied.

73  Alberto  I2PHD
P.S. In the beginning Winrad did not have this compensation. But when the number of emails asking for it surpassed a 
given threshold, well, I was somehow forced to implement it....:-)


#############################################################
This message is sent to you because you are subscribed to
 the mailing list <linrad@xxxxxxxxxxxxxxxxxxxxx>.
To unsubscribe, E-mail to: <linrad-off@xxxxxxxxxxxxxxxxxxxxx>
To switch to the DIGEST mode, E-mail to <linrad-digest@xxxxxxxxxxxxxxxxxxxxx>
To switch to the INDEX mode, E-mail to <linrad-index@xxxxxxxxxxxxxxxxxxxxx>
Send administrative queries to  <linrad-request@xxxxxxxxxxxxxxxxxxxxx>


LINRADDARNIL